What's the first issue the new President needs to address for the active military when he/she takes office?

The economy. Without a robust American economy none of the problems confronting the military and defense can be addressed adequately. Inasmuch as the government can do little to make the economy better, the best it can do is get the hell out of the way and let We the People fix it. All we need from the government is minimal regulatory laws and effective and fair application of them so that We the People compete on a level playing field. Then stand back and watch what we can do (just as our forefathers did before the government decided they knew better).

First issue should be one of many. Get the help the military veterans need. Not have to wait over 30 days for a Dr. Appointments. Take care of homeless veterans (If they want help). Quit trying to get rid of the benefits we have worked many years for.
Take care of the active force. Taking away BAH money is not taking care of them. Better training, up-to -date. In some cases, the training is not always on the newest equipment. More research is needed on newly acquired equipment (try before you buy may be an option). Pay raises should be at least 3%.
Do we really need to waste time and money on what color our PT socks are?
The military vets should always be our number one priority. Without them, there would not be a United States.
We have spent enough time and energy on the sexual orientation of the force. We may not all agree with the outcome but we are all in this together now. We need more attention on being Soldier/Sailors/Marines/Airman and not on who we prefer to be or get married to. Hooah!

There is a ton of stuff for the next POTUS.
Leave or improve the retirement pay system - if your going to ask so much of people don't try and screw them in the end. There needs to be a carrot of some sort.
Prepare the younger Americans for their future - 22% can't pass the ASVAB and somewhere in the neighborhood of 72% are disqualified because they are too fat, too weak or too stupid.
Modernize equipment for tomorrow's conflicts, not today's realizing that there is no cheap alternative but in that there it is inexcusable to inflate costs or waste funds.